CryptSetHashParam

The CryptSetHashParam function, in theory, customizes the operations of a hash object. Currently, only a single parameter is defined for this function.

#include <wincrypt.h>
BOOL WINAPI CryptSetHashParam(
  HCRYPTHASH hHash,  // in
  DWORD dwParam,     // in
  BYTE *pbData,      // in
  DWORD dwFlags      // in
);

Parameters

hHash: Handle to the hash object on which to set parameters.
dwParam: Parameter number. See the "Remarks" section for a list of valid parameters.
pbData: Parameter data buffer. Place the parameter data in this buffer before calling CryptSetHashParam. The form of this data will vary, depending on the parameter number.
dwFlags: Flag values. This parameter is reserved for future use and should always be zero.

Return Values

If the function succeeds, the return value is TRUE. If it fails, the return value is FALSE. To retrieve extended error information, use the GetLastError function.

The following table lists the error codes most commonly returned by the GetLastError function. The error codes prefaced by "NTE" are generated by the particular CSP you are using.

Error code	Description
ERROR_INVALID_HANDLE	One of the parameters specifies an invalid handle.
ERROR_BUSY	The CSP context is currently being used by another process.
ERROR_INVALID_PARAMETER	One of the parameters contains an invalid value. This is most often an illegal pointer.
NTE_BAD_FLAGS	The dwFlags parameter is nonzero or the pbData buffer contains an invalid value.
NTE_BAD_HASH	The hash object specified by the hHash parameter is invalid.
NTE_BAD_TYPE	The dwParam parameter specifies an unknown parameter.
NTE_BAD_UID	The CSP context that was specified when the hKey key was created cannot be found.
NTE_FAIL	The function failed in some unexpected way.

Remarks

The dwParam parameter can be set to one of the following values:

HP_HMAC_INFO. The pbData buffer should contain a pointer to an HMAC_INFO structure that specifies the cryptographic hash algorithm and the inner and outer strings to be used.
HP_HASHVAL. Hash value. The pbData buffer should contain a byte array containing a hash value to place directly into the hash object. Before setting this parameter, the size of the hash value should be determined by reading the HP_HASHSIZE parameter with the CryptGetHashParam function.
Some CSPs will not support this capability. Occasionally, it is convenient to sign a hash value that has been generated elsewhere. This is the usual sequence of operations:
1. The application creates a hash object with CryptCreateHash.
2. It specifies a hash value by setting the HP_HASHVAL parameter.
3. It signs the hash value by using CryptSignHash, obtaining a digital signature block.
4. It destroys the hash object by using CryptDestroyHash.

Note Some CSP types may add additional parameters that can be set with this function.

Example

// EXAMPLE CODE FOR USING CryptSetHashParam
// Set up the variables.
HCRYPTHASH     hHash;      // A handle to the hash object on which to set
                        // parameters
DWORD       dwParam;    // dwParam- paramater # can be HP_HMAC_INFO-
                        // initialized elsewhere
BYTE        pbData[16]; // The parameter data buffer
DWORD       dwFlags = 0;// set to zero
BOOL        Return;
Return = CryptSetHashParam(hHash, dwParam, pbData, dwFlags);
if (Return) {
 cout<< "function succeeds"<< endl;
}
else {
 cout<< "retrieve error"<< endl;
}

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